The public spending watchdog will be asked to investigate a multimillion-pound IT blunder that has left army recruitment in crisis.

Philip Hammond, the Defence Secretary, was under pressure last night to clarify the scale of the cost attached to the botched computer system, which is at the centre of the Government’s attempt to save money by laying off regular soldiers and hiring reservists.

He told MPs on Tuesday that only £4.5 million was needed to pay for a replacement. It is understood, however, that the options available to the Ministry of Defence have been either to spend an extra £43